Fettisdagen literally means 'fat Tuesday' (fett + tisdag), and it is the Swedish name for the Catholic celebration of Shrove Tuesday or Mardi Gras, being a literal translation of the latter.
In 2021, it takes place on February 16th.
In Catholic tradition, this is the final day of Shrovetide, the period of confession and reflection before Lent, forty days of fasting or abstinence from luxuries. People would also use the final day before fasting to indulge in rich foods, hence the 'fat'.
In Sweden, which is predominantly secular, the day has mostly lost its religious connotations, and it's not a public holiday.
But the Swedes are not likely to pass up an opportunity to enjoy baked goods.
So the food-related part of the tradition has stuck around, and to most people in the country Fettisdagen is simply a chance to eat semlor: wheat, cardamom-spiced buns filled with almond paste and lots of whipped cream. In fact, the day is sometimes referred to simply as semmeldagen or semlans dag.
Många svenskar äter minst en semla på fettisdagen
Many Swedes eat at least one semla on Shrove Tuesday
Snart är fettisdagen här
Shrove Tuesday will soon be here